These fish are mostly found in river estuaries or mangrove swamps in the wild, and some in large pieces of Brackish water including the Baltic Sea, Black Sea and the Caspian Sea. Some will also venture, and may cope, in Freshwater or Marine conditions. Brackish water has more salt content than Freshwater, but less than Saltwater, usually between 0.5 and 30 grams of salt per litre.